Scheduling of DSP data flow graphs with processing times characterized by fuzzy sets

In recent years a great deal of research has been conducted in the area of scheduling DSP data flow graphs onto multiprocessing systems. Most of the static scheduling techniques assume the worst case or the best case computational delay of the functional units used in the target architecture. This assumption is not realistic, since some of the computational times of the DSP tasks may be imprecise due to the fact that during early design phases, the characteristics of the final implementation of the functional units are not be known. In this paper, the impreciseness of the processing times of the functional units is taken into consideration by considering them as fuzzy sets, and then using fuzzy arithmetic to build the time schedule. The range of control steps (mobility) which represents the possible firing times of a task is determined, and a fuzzy rule base is employed to infer the degree of acceptability in selecting a certain control step within this range.